It is well known to tag petroleum fuels with "silent" markers so that the fuels can be identified for tax purposes, source of manufacture, brand identification and dilution or adulteration. Such markers are added to the fuels at low levels, typically at levels of 100 ppm or below, where they are not readily detectable with the naked eye. However, as it is necessary to be able to easily detect the presence of such markers, a simple chemical test must be available for their detection.
Generally the chemical test involves an extraction with either an acidic aqueous medium or an alkaline aqueous medium accompanied by reaction with a chromophore-producing reagent. As such, markers used to tag petroleum fuels must be readily miscible with the hydrophobic fuel, but in the presence of either hydrogen ion or hydroxyl ion become highly preferentially soluble in the respective aqueous medium. The chromophore-producing reactant may be the acid itself, such as with the markers described in U.S. Pat. No. 5,490,872, the teachings of which are incorporated herein by reference; the base itself, such as with the markers described in U.S. Pat. No. 5,205,840, the teachings of which are incorporated herein by reference, or an additional agent, such is the case with the markers described in U.S. Pat. No. 4,209,302 where the marker is reacted with a diazo compound contemporaneously with or subsequent to extraction with an acidic aqueous medium. The present invention is particularly directed to those dyes which are extractable with an acid or a base and in which the acid or base develops the color in the marker.
Extractions, particularly in the field, involve liquids that can leak or spill. Furthermore, liquids present a disposal problem. In order to ensure a complete separation of the petroleum and aqueous phase, it is conventional to include surfactants in the extraction solution. As a result, the sampled petroleum fuel is contaminated and cannot be returned to its source. Accordingly, the entire extraction mixture, including both the aqueous phase and the petroleum fuel phase must be stored and transported for subsequent proper disposal. Furthermore, separation of immiscible layers into clear, homogeneous phases may be relatively slow, depending on the specific components of the aqueous/non-aqueous system, taking from 5 to 15 min., which typically results in "dead time" for the tester. The volume of liquid needed for extraction can be large due to low concentration of the marker. Also, concentration of dilute marker by evaporating liquid is time-consuming.
Because of the inconvenience of liquid extractions, resin column testing for markers have been proposed. U.S. Pat. No. 5,304,493 describes extracting a fuel specimen tagged with an anthraquinone dye in a column of unbonded silica followed by eluting the dye with a solvent, such as toluene or dichloromethane. Like extraction, however, this method can be time-consuming and produces waste solvents which must be disposed of. U.S. Pat. No. 5,244,808 describes a three-resin column test for detecting markers of the type described in above-referenced U.S. Pat. No. 4,209,302.
The present invention is directed to a quick, simple test for the identification of petroleum fuel markers which minimizes disposal problems and is non-destructive of the specimen being sampled.